Modern electric vehicles such as, for example, vehicles which are driven exclusively by means of electrical energy, but also hybrid vehicles which have combinations with internal combustion engines or fuel cells, are often equipped with one or more electrochemical and, if appropriate, additional electrostatic energy stores. Both electric vehicles and hybrid vehicles are referred to as electric vehicles in this disclosure.
Electrochemical energy stores can be, for example, lead acid batteries, nickel metal hybrid batteries, nickel zinc batteries, lithium ion batteries or else combinations of these batteries. Combinations with double layer capacitors can also be used.
In order to charge such energy stores with energy, a charging process by means of a charging device may be necessary. In the case of an electric vehicle, such a charging device can be a stationary charging device or a charging device which is integrated into the electric vehicle, referred to as an on-board charger.
Each energy store is typically subject to an aging process depending on its mechanical and chemical structure. The speed of this aging process can depend on different factors, in particular on a charge state, a temperature, charging currents and discharging currents, and on charging ranges and discharging ranges during the operation of the energy store.
The degree of influence of these factors on the aging process of an energy store may depend on an operating state of the energy store. In particular, in the case of an electric vehicle the operating state of driving (cyclical aging) and that of parking (calendar aging) must always be considered separately from one another.
In the case of lithium ion batteries in an electric vehicle, for example in the operating state of parking in particular the charge state and the temperature are often decisive factors for the speed of the aging process of the energy store. A high charge state of over 60% with respect to the fully charged state at simultaneously high temperatures has a particularly unfavorable effect on the service life of such an energy store. Such conditions can, however, occur frequently since the parking constitutes on average 95% of the overall service life of a vehicle (in the case of a passenger car).
If an excessively high charge state during a parked state is therefore unfavorable for a long service life of such an energy store, in particular at high temperatures, this may run counter to a requirement for a high power level or a large quantity of energy which can be retrieved at any time, for example in the form of a large range in the case of an electric vehicle.
In addition, the case of planned extraction of power from the energy store occurring several days, or longer, into the future may be particularly problematic because the temperature profile is unknown until then. This makes the decision as to how an optimum charge state of the energy store is to be set in order to ensure the longest possible service life of the energy store more difficult.
Furthermore, the duration of a charging process cannot always be anticipated with sufficient accuracy since the network utilization factor of a power supply network in the future may be different from an instantaneous network utilization factor. For this reason, the problem of the optimum starting time of a charging process arises, which starting time should, furthermore, also depend on the planned extraction of energy in order to slow down the aging of the energy store as much as possible.
A power network, by means of which power suppliers make available electrical energy, is referred to herein as a power supply network. This may generally be a domestic network but, in particular, may also be a specific high power network which is suitable for particularly high power consumption levels, such as may occur during a charging process of an energy store in an electric vehicle.
The charging device may therefore be intended to lower the operating costs during the use of the energy store and at the same time permit the highest possible level of comfort of use, accompanied by the longest possible service life of the battery. Furthermore, a lengthened service life of the energy store may also permit environmental protection requirements to be taken into account. In order, as far as possible, to correspond in principle to these requirements which are becoming ever more important so that it is also possible to cope with the growing requirements in future, the charging device should help to facilitate the use of renewable energies which are already fed into the power supply networks by various power providers.
In addition, it may be expected in the future that for environmental-policy purposes current for electric vehicles will receive favorable tax treatment or that more favorable power tariffs will be provided for electric vehicles than for other consumers. A modern charging device should therefore make it possible to permit the user to select power tariffs which are particularly favorable and/or to enjoy tax benefits. In addition, large charging currents during the charging process may lead to additional stressing of the supply network, in particular at peak load times of the supply network. In particular, relatively high power prices can generally be expected at such peak load times.
Modern charging devices frequently contain programmable computing units with which, for example, switching on intervals or switching off intervals for charging processes can be programmed, for example in order to facilitate the use of favorable off-peak electricity at night. The programming is usually done manually or by means of a PC, which is frequently very awkward or even impossible if there is no PC available. The same applies to programmable devices which are connected to the energy store.